This invention relates to pressurized thermal systems that regulate human core temperature by convecting pressurized, thermally regulated air. More particularly, the invention relates to inflatable thermal blankets and the like that are used, for example, in a medical setting to deliver a bath of pressurized air which is heated, cooled, or ambient temperature, for the treatment of hypothermia or hyperthermia. In particular, pressurized, thermally regulated air is used to inflate such a device and is expelled therefrom onto a person or animal. Still more particularly, the invention relates to monitoring the operation of a pressurized thermal device in order to detect and respond to a potentially hazardous condition of its operation. Further, the invention relates to the identification of an inflatable thermal device and controlling the delivery air in response to the identification so that special services can be provided based on patient identity or inflatable device model number.
The International Electrotechnical Commission has promulgated a new standard (IEC 601-2-35) entitled Particular requirements for safety of blankets, pads and mattresses, intended for heating in medical use. This standard imposes requirements on the design and operation of convective warming systems. In particular, clause 46.101 states: xe2x80x9cIf omission of a part, or the interchange of parts of a multi-part heating device, will cause a safety hazard, the heating device shall be designed such that heat will be supplied only if all parts of the heating device are correctly positioned.xe2x80x9d This requirement is intended to prevent human or equipment error leading to patient injury.
In convective warming systems, a pressurized thermal device is used to deliver a bath of pressurized, thermally-regulated air to a person, animal, or thing. The device is inflated with the pressurized, thermally-regulated air and has one or more surfaces adapted for expelling the air onto a person. Such devices may lie on a person, around a person, or under a person. U.S. Pat. Nos. 5,324,320 and 5,405,371, for example, describe inflatable thermal blankets that lie on a person, expelling pressurized, warmed air through a lower surface that faces the person. U.S. Pat. No. 5,300,101 describes another inflatable thermal device that lies around the sides and at least one end of a person. Other kinds of inflatable thermal devices are contemplated, including those lying under a person. Therefore, when used, the term xe2x80x9cinflatable thermal devicexe2x80x9d is intended to invoke any and all blankets, pads, mattresses, covers, and equivalent structures that operate as just described.
Typically, the inflatable thermal devices of interest convect pressurized air in response to a pressurized flow of warmed, cooled, or ambient temperature air that is provided, for example, from a heater/blower unit through an air hose. Typically the inflatable device includes one or more inlet ports that receive one end of the air hose. The other end of the air hose is received in the heater/blower unit. When the heater/blower unit is turned on, air is warmed in the unit and pumped from the unit through the air hose to inflate the inflatable thermal device, whence the air is exhausted to warm or cool a person. Such devices may exhaust the air through a plurality of punched holes, through porous material, or through air permeable material.
One hazard in convective warming systems that use inflatable devices is the risk of overheating or burning a person. In the first instance, the air temperature may exceed a level necessary for proper treatment. In the second instance, the end of the air hose that is received in an inlet port may become dislodged and repositioned in such a way as to direct the pressurized, heated air flow directly onto a person. It is these hazards that are contemplated by the IEC standard. To date, means for detecting and mitigating these hazards have not been incorporated into the convective warming systems described above. Furthermore, in addition to the hazards contemplated by the new IEC standard, there is an operating deficiency common to many commercially available convective warming systems. This deficiency lies in the dependence of the air flow temperature at the distal end of an air hose on several environmental and design conditions which prevent accurate estimation of air hose outlet temperature.
The commercially available heater/blower units for convective warming systems include a heater and a blower which operate to provide a steady stream of temperature-conditioned air at a given mass flow. The temperature of the heated air ducted from the heater/blower unit through an air hose is tightly controlled at the heater/blower unit end of the air hose; however, the temperature of air flow introduced into the inflatable thermal device is a function of several factors, including, but not limited to: 1.) the thermal capacity of the unit; 2.) the blower capacity; 3.) the length, thermal conductivity, and thermal emissivity of the air hose between the unit and the device; 4.) the fluid flow resistance of the device; and, 5.) the ambient conditions, of which temperature and external air velocity are the most important.
The exhaust (output) temperature of the flow of air leaving a heater/blower unit is generally tightly controlled by a unit temperature controller. The temperature controller continually senses the output temperature at a port in the unit where the proximal (near) end of the air hose is received and adjusts the heater unit power to maintain the output temperature at constant setting. The temperature of the air flow at the distal (far) end of the air hose (that is, the inlet temperature to the inflatable thermal device), however, depends greatly on the conditions listed above.
None of the commercially-available convective warming systems have sensors in the inlet port to measure air flow temperature, which can result in uncertain and poorly controlled delivery of therapy. Some prior art devices, including devices made by the assignee of the instant application, have equipped the distal end of the air delivery hose (connected to the inlet port) with temperature sensors. However, these sensors can still be inaccurate, as they provide inaccurate readings if the hose is improperly connected to the inlet port.
With most of the presently available heater/blower systems, it is also possible to interconnect the blower units, hoses, and thermal blankets of different manufacturers. Because these components may not have been designed to work together, and because there are not always common standards, the patient can be inadvertently supplied with air at inappropriate flow rates and temperatures. Not only can the patient be harmed, it is also possible to damage the equipment. Further, some users may knowingly use equipment that is not designed to work together out of convenience. Clearly visible electrical contact points permit operators to bypass interlock safeguards. The concern for the improper use of equipment must be tempered with the ability to warm patients in emergency situations.
Accordingly there is a need to: 1.) prevent heater/blower unit misuse when the inflatable thermal device has been disconnected from the air hose; 2.) provide better control of air flow temperature at the distal end of the air hose irrespective of ambient conditions, resistive load of the inflatable thermal device, or heater/blower unit capability; and 3.) meet the requirements of the IEC standard.
The invention is based on the critical realization that the junction between the distal (far) end of an air hose and an inlet port of an inflatable thermal device provides a location where the continuity of the air flow path and the magnitudes of air flow characteristics such as temperature and pressure can be sensed or regulated. In this regard, a first circuit element may be provided that is integral with the pressurized thermal device at, in, or near an inlet port, while a second circuit element may be provided at, in, or on the distal end of the air hose. When the distal end of the air hose is received in the inlet port, the first and second circuit elements cooperate to provide a signal indicative of connection between the inlet port and the distal end. When the distal end of the air hose is not connected to the inflatable thermal device by way of the inlet port, the signal cannot be generated. Therefore, the presence or absence of the signal may be used to provide an indication of a connect/disconnect condition between the inlet port and the distal end of the air hose. Moreover, the information can be enriched by addition of one or more sensors at or near the junction between the inlet port and the distal end of the air hose to provide an indication of one or more air flow characteristics such as temperature or pressure, or both. It may be desirable to provide a power override function that turns off the heater/blower unit, modulates the temperature output of the unit, or places it in a standby condition in response to either a disconnect condition indication or measurement of a temperature and/or pressure at the distal end of the air hose that deviates from a predetermined value.
In particular, the above-described invention is made more useful by making the insertion of the distal end of the air hose into the inlet port independent of any kind of rotational alignment, so that the operators does not need to take the time to align keys. The rotational independence of the connection permits the air hose to be rotated while in use without breaking the electrical connection between the first and second circuit elements. The inlet port first circuit element can be of a conductive annular ring, a hose card with a conductive ink surface, or a wireless communications radiator. The invention is also made more useful by using the first and second circuit elements to communicate the identity of a specific inflatable thermal device. In one aspect, electrical impedance is measured to determine an inflatable device type to determine air flow characteristics. In another aspect, the first circuit element is connected to an electronic identification tag to provide information such as device model number and patient identification.
In yet another aspect of the invention, flow of air to the inflatable thermal device is controlled mechanically, with the insertion of the distal end of the air hose into the inflatable thermal device. Several valve mechanisms can be used to block air flow from the air hose when the hose is not properly seated in the inlet port. When inserted, the valves are forced open to provide air to the inflatable thermal device.
Accordingly, it is an object to invent a convective warming system that includes a pressurized thermal device with the ability to sense and react to air flow conditions at a point where an air flow is provided through an inlet port of the device.
Another object is to disable, prevent, or attenuate the operation of a convective warming system when the inflatable thermal device becomes detached from a heater/blower unit.
Another object is to identify the inflatable thermal device, and to modify the flow of air, air temperature, or both, in response to the identification.
Another object is to determine the number of times the pressurized delivery device (blanket) is used or connected to the heater/blower unit.
These and other objects and advantages of this invention will become evident when the following detailed description is read in conjunction with the below-described drawings.